246 VERTEBRATE ZOOLOGY 



leaves, which are piled up into a mound and then hollowed out into 

 a receptacle not unlike a huge bird 's nest. The eggs are about three 

 inches in length and of an oval shape and are laid to the number of 

 twenty to thirty to a nest. 



The most typical crocodile is the classic Crocodilus niloticus (Fig. 

 137, B), the Nile crocodile, which is believed to be the " leviathan" of 

 the Book of Job. The armor is exceedingly heavy and impenetrable 

 to any weapons but bullets. The crocodile makes a long tunnel-like 

 burrow thirty to forty feet in length, with an opening below the water 

 level, used as an entrance, and with a large chamber at the inner end 

 well above the water level. The nest is large and flask-shaped like 

 that of some tortoises, but with a flat bottom grooved around the 

 periphery, causing the eggs to lie in a circular ring. The mother lies 

 over the covered-up nest and takes considerable care of the young 

 after they have hatched. 



ORDER SAURIA (SQUAMATA) LIZARDS AND SNAKES 



The lizards and snakes to-day are playing much the same role for 

 the reptiles that is played by the frogs and toads for the Amphibia. 

 They represent climax conditions and exhibit very pronounced 

 adaptive radiation, being in both groups terrestrial, fossorial, arboreal, 

 amphibious, and aquatic. 



They are characterized by the possession of: a movable quadrate 

 bone, which enables the mouth to open more widely; a transverse 

 cloacal aperture; and double copulatory organs. 



Contrary to the generally accepted idea that they have arisen 

 from some ancestral prosaurian like Sphenodon, they are now traced 

 back to the early lizard-like group represented by Varanops (Fig. 

 123, A) of the Permo-Carboniferous. This ancestral type has been 

 called by some authors Proterosauria and was probably ancestral to 

 all of the Sauria or Squamata, past and present. 



DIVISION I. LACERTILIA (LIZARDS) 



It now appears that the lizards have stolen the laurels of Spheno- 

 don, the reputed prototype of all the reptiles; for the earliest known 

 reptile of the Permo-Carboniferous was a very generalized and de- 

 cidedly lizard-like creature. Some of the modern lizards have de- 

 parted very little from that type. Perhaps this is the secret of their 



